Micromechanical and Macroscopic Modelling (MMM)
Prof. Dr. Alexander HartmaierDeveloping innovative materials that meet the complex requirements of a diverse range of applications is only possible if the relation between their inner structure, i.e. the microstructure, and their properties is thoroughly understood. We aim at deriving such microstructure-property-relationships to predict macroscopic mechanical properties of materials, like strength, hardness, and toughness, by employing the methods of computational materials science and multiscale modelling. To accomplish this, we typically start from macroscopic models that describe an engineering application or test (see Figure 1). At the critical spots of this macromodel, where the conditions are particularly severe and potentially damaging, a micromechanical model is employed that explicitly takes into account the local microstructure and loading conditions.
Figure 1: Top-down scalebridging approach demonstrated for a NACE-A test specimen that is subjected to a sour environment under a mechanical load of 85% of its yield strength. At the positions where the corrosive attack creates microcracks at the surface, a micromechanical model (RVE) is considered. The microstructure in such micromechanical models can be described on various scales or levels of precision.
The microstructure in such micromechanical models is described by representative volume elements (RVE) that can be developed on different purpose-specific levels of detail, to represent either phases as homogeneous regions or individual grains within phases or even sub-structures within grains (see Figure 2). Such micromechanical models serve mainly two purposes: (i) they provide insight into the critical deformation and failure mechanisms and how they depend on the microstructure and local thermal, mechanical, and chemical conditions of the material; (ii) they serve as the basis for the macroscopic descriptions of material properties in form of flow rules as they are used in continuum plasticity. This latter step of developing macroscopic flow rules based on micromechanical models is termed homogenization and can be used to take microstructural properties and mechanisms implicitly into account in macroscopic models of engineering problems.
In some situations, it is necessary to refine our microstructural description even to the level of individual (discrete) dislocations and their interactions with the microstructure. Such discrete dislocation dynamics (DDD) models are, for example, employed to study the deformation and creep behaviour of single crystal superalloys within the DFG-funded Collaborative Research Centre “From Atoms to Turbine Blades” (see Figure 2). Finally, process on interfaces such as interface sliding or cracking can only be understood on the atomic scale. Hence, such atomic models of interfacial properties must be analysed closely (see Figure 3), and their results need to be homogenized in order to be applicable in cohesive zone models or other fracture and damage models that can be applied on the macroscale.
The groups of the department are:
A list of research projects currently offered in the department of Micromechanical and Macroscopic Modelling (Prof. Hartmaier) can be found here